The authors present a graph that shows the relative rates of change in the glacier in terms of advance and retreat since 10,000 years ago.

From about 8,000 to 4,000 years ago (during the Holocene Climate Optimum) it was too warm for a glacier to form.

After about 4,000 years ago, a glacier formed and began a series of advances and retreats up to the present as shown in their graph.

I plotted their graph and then wondered what it would look like if I accumulated the advances and subtracted the retreats. The figures are relative and not absolute. Thus the resulting curve shown below does not tell us the total mass of the glacier at any point but merely indicates how the glacier grew in mass from 4000 years ago (2000 BC) to its greatest extent around 1200 years ago (800 AD), then began to lose mass until the Medieval Warm Period around 1000 years BP.

After 1000 years BP the glacier gained mass during the Little Ice Age, which ended around 200 years ago. Since then the Earth’s climate has been getting warmer and the glacier has retreated again. Still the glacier seems to have a long way to go before reaching its extent at the end of the Roman Warming Period around 1500 years ago.

Points to Note

1.Declines in the curve correspond to increasing total ice mass and thus cooling.

2. It can be seen that the shape of the curve for the 2000-year period from 4000 BP (before the present) to 2000 BP is similar to the shape of the curve for the 2000-year period from 2000 BP until the present. The correlation coefficient is 0.78 and R-squared is 0.60 with 21 pairs of data, significant at the 1% level of confidence.

3. The glacier gained mass after 4000 years before the present (BP) and then lost it by 38oo BP, a date that corresponds to the Minoan Warm Period. The glacier then gained mass until about 3200 BP a time that corresponds to the end of Mycenaean civilization.

4. The glacier then lost mass during the period 1200 BP to 1500 BP, a period that corresponds to the Roman Warm Period.

5. The glacier gained mass for 300 years after 500 AD (1500 BP) during which Roman civilization declined.

6. From around 700-800 AD (1200 BP) to 1000 AD (1000 BP) the glacier lost mass due to warming. This would correspond to the Medieval Warm Period in Europe.

7. During the period from 1500 BP to 1000 BP the general increase in mass of the glacier was reversed by a significant glacier retreat around 1300 BP, before retreating to its furthest point around 1000 BP. This indicated that cooling was not uniform between 1500 and 1000 BP, but broken by a warm interval around 700-800 AD.

8. After 1000 AD the glacier gained mass during the period known as the Little Ice Age, a gain that was reversed by warming after about 1800 AD.

9. Since 1800 AD (200 BP) the glacier has recovered mass lost since the year 1000 AD but has not yet recovered the mass lost since 700-800 AD (1350 BP).

Uncertainties

It is not certain to what extent changes in glacier mass are driven by changes in temperature or changes in precipitation.

Wind blowing over a glacier can cause sublimation of ice directly to vapour without an intervening liquid stage. The mount Kilimanjaro Glacier is known to respond to wind in this way. Whether or not the Kulusuk Glacier has responded this way is apparently not known. If so, the mass of the glacier would be less than expected from melting caused by temperature change.

Therefore this attempt at correlation between the mass changes of a Greenland glacier and European climate is merely suggestive. Nevertheless, the analysis is consistent with that of H. H. Lamb.

As for the Greenland settlements about 1000 AD, it seems that Greenland may have recovered from the very severe climate conditions that prevailed 200 years before settlement began in 985 (1030 BP) and by around 1000 AD appeared suitable for settlement.

The settlers could not have known that climate would deteriorate for hundreds of years during the Little Ice Age, just as we do not know if climate will again deteriorate and the glaciers again advance.

“We do not believe any group of men adequate enough or wise enough to operate without scrutiny or without criticism. We know that the only way to avoid error is to detect it, that the only way to detect it is to be free to inquire. We know that in secrecy error undetected will flourish and subvert”. - J Robert Oppenheimer.